This allows the camera to be positioned away from the door by running a single cable. Without this, you'd need one for power, one for network, AND one for the I/O pins. Using a single 24ga wire for power is suboptimal, but the camera doesn't draw much power, and it hasn't been an issue yet.

In the box above the door:
Ethernet pins pass through to Ethernet input (into which is plugged the feed from the back of the space.)
GND from power input goes to GND from camera, also to LED cathode and SSR negative.
+12 from power input goes to +12 from camera, also to switch contact.
Relay Output from camera goes to LED anode and SSR positive.
Digtal Input + from camera goes to switch contact. SSR isn't currently connected; signals are on orange wires, shrinkwrapped to prevent shorts in the time being.

(To accommodate a future local OPEN sign, provision has been made for connecting the big solid-state relay, which can switch anything we could throw at it.)